EUV Mask Blank Hard Mask Layer Design
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Solution Overview
Problem
In EUV lithography, achieving high resolution patterns is hindered by the limitations of conventional resist film thickness and etching selectivity, with crystalline hard mask layers and high surface roughness leading to large line edge roughness and reduced pattern accuracy.
Innovation Solution
A reflective mask blank with an absorber layer containing tantalum (Ta) or palladium (Pd) and a hard mask layer composed of chromium (Cr), nitrogen (N), and hydrogen (CrNH or CrOH films) is developed, ensuring high etching selectivity and amorphous state with low surface roughness to enhance pattern resolution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the resist film is made thin to achieve high resolution patterns, then the pattern resolution is improved, but the etching accuracy deteriorates because the resist film is consumed in the etching process
Solution Approach 1:
The patent divides the single resist film into two functional layers: a thin resist film (50-150 nm) for defining high-resolution patterns and a thick hard mask layer (100-300 nm) for protecting the pattern during etching. This segmentation allows each layer to perform its specific function optimally without compromising the other.
Solution Approach 2:
The hard mask layer is formed in advance on the absorber layer before applying the resist film. This preliminary action creates a protective foundation that prevents direct contact between the etching process and the absorber layer, thereby preserving pattern accuracy throughout the etching process.
2Reliability
If a conventional hard mask layer is used to protect the absorber layer during etching, then the etching selectivity is improved, but the line edge roughness increases due to crystalline structure and high surface roughness
Solution Approach 1:
The patent changes the physical and chemical parameters of the hard mask layer by selecting specific materials (silicon oxide, silicon nitride, or silicon oxynitride) and controlling their deposition conditions to achieve amorphous structure with low surface roughness (Ra ≤ 0.5 nm). This parameter optimization maintains high etching selectivity while minimizing line edge roughness.
Solution Approach 2:
The patent uses composite material systems where the hard mask layer is formed from silicon-based compounds (SiO2, Si3N4, or SiOxNy) that combine the benefits of high etching selectivity against tantalum-based absorber layers with amorphous structure and low surface roughness, avoiding the crystalline structure problems of conventional materials.
3Reliability
If a thick resist film is used to maintain etching accuracy, then the etching accuracy is improved, but the pattern resolution deteriorates
Solution Approach 1:
The patent segments the protective function from the pattern-defining function by creating a separate hard mask layer that handles etching protection while allowing the resist film to be optimized for high-resolution pattern formation with minimal thickness.
Solution Approach 2:
The hard mask layer acts as an intermediary between the resist film and the absorber layer, providing the necessary protection during etching without interfering with the pattern formation process. This mediator allows the use of thin resist films while maintaining both pattern resolution and etching accuracy.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution allows for thinner resist films while maintaining high etching selectivity and reducing line edge roughness, enabling the creation of high-resolution patterns with improved accuracy.
Implementation Method 1
a content of H is from 0.1 to 15 at %
Data Source
AI summary
To provide an EUV mask blank with which the etching selectivity under etching conditions for absorber layer is sufficiently high, line edge roughness after pattern formation will not be large, and a pattern with high resolution can be obtained.A reflective mask blank for EUV lithography comprising a substrate, and a reflective layer for reflecting EUV light, an absorber layer for absorbing EUV light and a hard mask layer formed in this order on the substrate;wherein the absorber layer contains at least one of tantalum (Ta) and palladium (Pd) as the main component;the hard mask layer contains chromium (Cr), either one of nitrogen (N) and oxygen (O) and hydrogen (H); andin the hard mask layer, the total content of Cr and either one of N and O is from 85 to 99.9 at %, and the content of H is from 0.1 to 15 at %.